Stock amp on my bike is 32 amps.
I want to add heated grips, some driving lights and maybe use a heated vest.
Is there a test I can do to find out how much if any capacity there is left?
I don't want to start draining the battery.
Thanks,
Chris

I have a 32 amps alternator and during the spring/fall I am riding with 2 50W driving lights + heated grips and heated vest.
I never had problems.
The easy way to find it, unplug your alternator and put a ammeter in line with the positive of the battery. Start your bike and turn on the light, 4 way flashers and brake lights you should not read more than 10-12 amps.
Driving lights, heated grips and vest should add an extra 10 amp load.

That's good to know. Do you know why BMW upgraded the alternator to 50 amps in the later years?

So the bike should be burning about 170 watts in normal use
with 200-280w. in reserve capacity?
(32amps x12v =384 w 32amps x 14v =450w)
Won't the RPM have an effect on the max output of the Alternator?

87m6chris wrote:That's good to know. Do you know why BMW upgraded the alternator to 50 amps in the later years?

It was upgraded for the police bikes.

87m6chris wrote:So the bike should be burning about 170 watts in normal use
with 200-280w. in reserve capacity?
(32amps x12v =384 w 32amps x 14v =450w)
Won't the RPM have an effect on the max output of the Alternator?

The alternator doesn't work under 1,500rpm

On the open road your proposed load should be no problem at all. If however you were going to be doing mostly city traffic driving where the revs were often below 2000 then I would suggest with your load you might have a problem and would need to reduce your electrical load. For touring, no worries go for it and have fun!

Regards,
K-BIKE

Thanks Guys, you just saved me $200 bucks. I should have known
BMW would build in more capacity for some frills.
Hope I can contribute one of these days.

You already did contribute because by asking the question someone else who wants to know the answer has just had it already answered, good on you for asking!
Regards,
K-BIKE